Roughly speaking, the second law of thermodynamics states that higher energy states move toward lower energy states; in simpler terms, differences in temperature, density and pressure want to even out. This is why articles such as balloons, tires and game balls inflated with air tend to go flat. Gas molecules under higher pressure within an inflated article aim to reach pressure equilibrium with air molecules surrounding the article until pressure equilibrium is reached. The air is set in motion by a pressure gradient force produced when air with different pressures are adjacent to one other.
A decrease in an article's inflation pressure causes the article to go flat thereby compromising the article's integrity and performance. Inflation pressures in articles may be lost, in part, due to seepage of gas molecules through the articles' surrounding cavity membrane or through their inflation valves. The loss of an article's inflation pressure through the membrane may be due to seam defects, defective materials or faulty constructive techniques of the article. In most cases, however, articles inflated with air lose pressure over time due to the small size of the molecules comprising air, which primarily includes the elements nitrogen and oxygen. These small molecules easily permeate the cavity membrane and gradually escape, thereby reducing pressure within the article.
Because of its availability, low cost, relative safety, and ease of use for inflation, air has been the most commonly used substance to inflate game balls requiring a gas fill. However, to combat loss of inflation pressure due to the permeation of small gas molecules through the membrane of a ball, inflation systems made up of larger, low permeability molecules such as fluoropropane (C3F8), hexafluoroethane (C2F6), and monochlorotrifluoromethane (CClF3) have been examined.
An alternate inflation system exhibiting improved pressure retention properties was disclosed by Koziol et al. in U.S. Pat. No. 4,098,504. The inflation system comprises a mixture of air and sulfur hexafluoride (SF6). Compared to other large molecule systems examined previously, SF6 was found to be substantially more suitable than other low permeability gases in terms of extended pressure retention, material cost, safety and availability.
However, an undesirable attribute of the use of the air and SF6 inflation system of Koziol in game balls, as well as with the use of other low permeability gas systems, is that balls in which it is used produce on impact, for example bouncing or striking the ball, unpleasant resonant frequencies described in the art as a pinging or ringing sound. While in no way interfering with the playability of the ball, many users considered the sound to be a distracting and annoying, thereby rendering the ball unsuitable for play.
In an attempt to ameliorate the noise resulting from the use of the air and SF6 inflation medium in a game ball, Reed et al. (U.S. Pat. No. 4,300,767) introduced free-moving materials to the cavity of a tennis ball to disturb the sonic resonance causing the “ping.” The materials tested as “ping” dampeners included: vermiculite, rubber dust, and foam and rubber cubes. Reed et al. discovered that the density of the materials made little difference on their performance as anti-ping materials; in fact, solid rubber samples of adequate size (≧1.2 cm cube) were effective. Reed et al. also found that metals, foam, dense rubber, fibers, and powders were all effective in reducing the “ping” noise if their volumes were large enough.
Ultimately, Reed et al. determine that a cube made of foam is the preferred “ping” suppression material and device. Although the cubed materials were found to adequately ameliorate the “ping” sound in tennis balls, the unattached free-moving cube compromises the playability of the ball. First, the free-moving cube inside the cavity of the ball alters the symmetry of the ball and could cause the ball to curve in midflight thereby changing its trajectory. Even a slight weight displacement can influence the ball's trajectory, which would be distorted even more so when a larger sized cube of greater weight was used. Second, although the movement and collisions of a free-moving cube in the cavity of a tennis ball may not be noticeable to one striking the ball with a racquet, a player is certain to feel the movement and collisions of an unattached cube in the cavity of a volleyball as it is set or received during play, or a basketball as it is caught or dribbled, or other handballs as they are used for other sports.
Furthermore, an unattached cube will no doubt wear down as it bangs around the cavity of the ball during play. The corners of the cube will round off, thereby decreasing its volume and changing its shape. As a result, over time the cube loses its “ping” dampening effectiveness prematurely with continued play.
Moreover, the cube in Reed et al. was disclosed only to work in a tennis ball. Scaling up this technology to work within a volleyball or a comparably sized ball would add significant weight to the game ball. The official weight, Pressure per Square Inch (PSI), and size of the ball is very tightly regulated by the various leagues and organizations that use the balls, such as the National Federation of State High School Associations, the National Collegiate Athletic Association, USA Volleyball, other Olympic teams, the Federation International de Volleyball, and other clubs, leagues, etc. As a result, weight equal in amount to that added by the noise dampening device as well as the SF6 must be removed from other components of the ball to offset their added weight. This can be accomplished by changing the material used for the interior surface of the exterior shell when an artificial shell material is used (the exterior surface itself is hard to change because it is meant to simulate leather or must be leather), using a thinner layer of leather, using a lighter bladder, or using a lighter valve assembly on the bladder. However, there is only so much that can be removed or changed in these sections and it may ultimately be impossible to fully compensate for the added weight of the cube and the SF6.
To account for the shortcomings in Reed et al., O'Neill et al. developed a technique described in U.S. patent application Ser. No. 11/363,618, whereby one or more acoustic pads were adhered to the interior wall of a game ball, such that the internal symmetry of the ball was not disrupted. The acoustic material preferably conforms to the internal symmetry of the ball and absorbs noise in the highest intensity region of the ball's inner cavity.
However, depending on the type of material used in construction, such pads may add the equivalent of a full layer of material to the ball in order to adequately muffle the noise while maintaining the internal symmetry of the ball. Adding that much acoustic material to a ball creates two problems. First, the pads and their adhesive add additional weight to the ball; and second a more complicated and time-consuming assembly process is necessary to construct the ball. Even if a smaller number of pads are added to the ball, it will still be necessary to glue or otherwise adhere the pads to an interior surface of the ball, which will increase the cost of components for the balls and more significantly increase the cost of manufacture. Adhesives also add unwanted weight to the ball.
Conventionally, game balls requiring a gas fill are inflated, if at all, either at the time of manufacture prior to shipping or by clerks at the individual retail stores. A ball that is filled completely with a large molecule gas system at the time of manufacture, such as those disclosed in Reed et al. and in O'Neill et al., is already compromised with regard to its longevity. Because the pressure within the ball is greater than the atmospheric pressure, the ball will naturally attempt to seek equilibrium, thereby forcing the smaller molecules of the gas used to inflate the ball to permeate the membrane of the wall to escape the higher pressure. Even when the gas filling the ball is comprised of larger molecules, those molecules will eventually find their way past the ball's membrane, causing it to lose pressure. This process is accelerated since Reed et al. and O'Neill et al. use a gas mix ratio that includes air, which is largely comprised of smaller molecules. A typical manufacturing to the end user time line is as follows:
Balls manufactured and stored at the manufacturer until ready for shipment—approximately one month;
Balls shipped to shipping company for transport to national distributor and to go through customs—approximately one to two months, including shipping (usually by cargo ship overseas);
Balls received by national distributor and warehoused pending orders from individual retail stores—one to three months;
Balls received by stores and stored in backroom until shelf space is available and ball is sold to an end user—one to three months.
Hence, the total amount of time that can pass between when a ball is manufactured and when it is finally purchased by an end user/consumer can range anywhere from seven months to eighteen months. Thus, significantly reducing properly pressurized retail shelf-life. The O'Neill et al. ball, which is inflated at the time of manufacture and is presently licensed to Spalding, provides a warranty to retain its inflated state for only a period of one year, which may have largely been passed before the ball is even purchased by an end user/consumer.
Furthermore, when a ball is inflated completely at the time of manufacture, it requires more container space during shipping, more warehouse space during distribution and warehousing, and more backroom shelf space at the retail store. All of this space costs money, increases the cost of shipping and distributing the balls on a per ball basis, and reduces the life expectancy of the balls.
On the other hand, balls that are shipped completely un-inflated run the risk of having their internal bladders seal shut during the long period between when they are manufactured and when they are finally inflated completely at a retail store. In addition, a completely un-inflated bladder is difficult for a retail clerk to fill without damaging the bladder from poking a pump needle through a wall of the bladder.
By partially inflating the balls at the place of manufacture prior to shipping, it would appear that the problems of the two extremes described above would be resolved. And, if the fill gas was air only, they would be. Hence, many air filled balls are shipped partially inflated. However, for game balls that feature a low permeability gas, such as SF6, as a fill component, the balls must be shipped fully pressurized and inflated because retail stores and end users do not have ready access to low permeability gases.